Imparting or improving water repellency of a substrate is desired for a number of substrates including organic or inorganic building components, for example, concrete, masonry, stucco, natural or artificial stone, ceramic, terracotta bricks, plaster board, fibre cement board, or other cement containing products, wood particle board, wood plastic composites, oriented strand board (OSB) or wood.
The desired water repellency properties are usually obtained by applying a water-repellent composition to the external surface of a substrate so as to create a water repellent coating on the substrate which protects this substrate from weathering and other deterioration. At least the outermost surface of building materials is treated in order to become waterproof.
Silicone compounds are used as water repellents due to their durability, good hydrophobicity and ease of application. First, silicone resins in solvent and methylsiliconates were used as silicone water repellent compounds. Then followed siloxane and silane based products in solvents. Next generation of water repellents is generally water based for environmental reasons and ease of use. The active ingredients contain siloxanes, silicone resins and silanes (and combinations of them). For example, U.S. Pat. No. 5,074,912 discloses a water repellent composition for treating porous substrates with an emulsion containing a siloxane which is a linear methylhydrogen-methylalkyl siloxane copolymer or a methylhydrogen-methylalkyl cyclosiloxane copolymer. However this product presents a Volatile Organic Content (VOC) of more than 100 g/l whereas emulsions having less than 100 g/l or even less than 50 g/l are desired.
WO200813423A1 describes silicone emulsions for imparting water repellency with a VOC content of below 100 g/l comprising phenylsilsesquioxane. The emulsions according to this disclosure lack however reactivity and depth of penetration in order to fulfil the requirement for long term protection of structural concrete or other porous building materials.